Sewage Sludge Compost Research Articles

Phytoextraction of As by Pteris vittata L. assisted with municipal sewage sludge compost and associated mechanism

Pteris vittata L. (PV), an arsenic (As) hyperaccumulator, has a potential to extract As from As-polluted soils. Since available As in soils can be taken up by PV, As fraction variation associated rhizosphere environmental characteristics caused by municipal sewage sludge compost (MSSC) could provide possible to strengthen As phytoextraction by PV. In this study, the mechanism of phytoextraction of PV aided by MSSC was revealed from aspect of environmental characteristics of rhizosphere soils and physiological properties of PV. The effect of MSSC on available As in soils was investigated by soil incubation experiment. Furthermore, the influences of MSSC on enzymes activities, communities of soil bacteria and fungi, As concentrations, and As fraction in rhizosphere soils of PV were explored, and then the biomass and As accumulation of PV were examined by greenhouse pot experiments. After 90 days, available As in soil incubation experiment significantly increased by 32.63 %, 43.05 %, and 36.84 % under 2 %, 5 %, and 10 % treatment, respectively, compared with control treatment. Moreover, As concentrations in rhizosphere soils of PV under 2 %, 5 %, and 10 % treatment decreased by 4.62 %, 8.68 %, and 7.47 %, respectively, compared with control treatment. The available nutrients and enzyme activities in rhizosphere soils of PVs were improved under the MSSC treatment. Affected by MSSC, the dominant phylum and genus for both bacterial and fungal communities didn't change, but their relative abundance increased. Additionally, MSSC significantly increased biomass of PV with corresponding mean ranging from 2.82 to 3.42 g in shoot and 1.82 to 1.89 g in root, respectively. And the concentrations of As in shoot and root of PV treated by MSSC increased by 29.04 %–144.7 % and 26.34 %–81.78 %, respectively, in relative to control. The results of this study provided a basis for MSSC-strengthened phytoremediation for As-polluted soils.

Common Bean Productivity and Micronutrients in the Soil-Plant System under Residual Applications of Composted Sewage Sludge.

Composted sewage sludge (CSS) is an organic fertilizer that can be used as a source of micronutrients in agriculture. However, there are few studies with CSS to supply micronutrients for the bean crop. We aimed to evaluate micronutrient concentrations in the soil and their effects on nutrition, extraction, export, and grain yield in response to CSS residual application. The experiment was carried out in the field at Selvíria-MS, Brazil. The common bean cv. BRS Estilo was cultivated in two agricultural years (2017/18 and 2018/19). The experiment was designed in randomized blocks with four replications. Six different treatments were compared: (i) four increasing CSS rates, i.e., CSS5.0 (5.0 t ha-1 of applied CSS, wet basis), CSS7.5, CSS10.0, CSS12.5; (ii) a conventional mineral fertilizer (CF); (iii) a control (CT) without CSS and CF application. The available levels of B, Cu, Fe, Mn, and Zn were evaluated in soil samples collected in the 0-0.2 and 0.2-0.4 m soil surface horizons. The concentration, extraction, and export of micronutrients in the leaf and productivity of common beans were evaluated. The concentration of Cu, Fe, and Mn ranged from medium to high in soil. The available levels of B and Zn in the soil increased with the residual rates of CSS, which were statistically not different from the treatments with CF. The nutritional status of the common bean remained adequate. The common bean showed a higher requirement for micronutrients in the second year. The leaf concentration of B and Zn increased in the CSS7.5 and CSS10.0 treatments. There was a greater extraction of micronutrients in the second year. Productivity was not influenced by the treatments; however, it was higher than the Brazilian national average. Micronutrients exported to grains varied between growing years but were not influenced by treatments. We conclude that CSS can be used as an alternative source of micronutrients for common beans grown in winter.

Insights into the formation and stability of soil aggregates in relation to the structural properties of dissolved organic matter from various organic amendments

Organic matter is an important determinant of soil aggregate formation and stability. However, the role of its structure, especially that of dissolved organic matter (DOM) from organic amendments (OAs), in the aggregation process remains imprecise. The purpose of this study was to understand the relationship between the chemical structure of water-extractable organic matter (WEOM), potential source of DOM from OAs, and their aggregate formation/stability functionality through model experiment. The WEOM samples were prepared from bark compost (BC), coffee residue compost (CRC), cattle manure compost (CMC), sewage sludge compost (SSC), fish cake (FC), and rapeseed oil cake (ROC) and characterized using high-performance size exclusion chromatography and 13C nuclear magnetic resonance and diffuse reflectance infrared Fourier transform (DRIFT) spectroscopies. An upland field soil was packed in glass columns and each WEOM solution or ultrapure water (Control) was applied repeatedly during a 30-day period. Aggregate size distribution (>2000, 500–2000, 250–500, 53–250, and <53 µm) was then measured and aggregate stability indices, mean weight diameter (MWD), and geometric mean diameter (GMD) were calculated. The addition of WEOM increased the distributions of soil mass and soil organic carbon (C) into the > 2000 µm aggregate fraction compared to Control treatment, and the ROC-, CRC-, and SSC-WEOM treatments resulted in greater MWD and GMD than Control and/or the other WEOM treatments. The % O-alkyl C (29–59% of total C) and the relative abundance of high-molecular-weight (HMW) fraction (>10 kDa; 2.3–7.1% of total) in WEOM correlated positively with the proportion of > 2000 µm aggregate fraction. The relative abundance of HMW fraction also correlated positively with MWD. These findings suggest that the high amounts of polysaccharides, suggested by % O-alkyl C and supported by DRIFT spectra, and/or other HMW components are desirable structural characteristics of WEOM for promoting macroaggregate formation and aggregate stability.

Environmental risks of organic fertilizer with increased heavy metals (Cu and Zn) to aquatic ecosystems adjacent to farmland in the northern biosphere of Japan

In Abashiri, Hokkaido, northern Japan, composted sewage sludge (CSS) containing a large amount of zinc (Zn) and copper (Cu) is used as fertilizer in agriculture. The local environmental risks of Cu and Zn from such organic fertilizers were studied. The study area, especially the brackish lakes located near the farmlands, is important for inland fisheries. The risks posed by heavy metals to the brackish-water bivalve, Corbicula japonica, was therefore investigated as an example. First, the long-term effect of CSS application in agricultural fields was monitored. Second, using pot cultivation, factors influencing Cu and Zn availability in the presence of organic fertilizers were evaluated under different scenarios of SOM content. In addition, the mobility and availability of Cu and Zn in organic fertilizers were evaluated in a field experiment. In the pot cultivation, both organic and chemical fertilizers increased the availability of Cu and Zn with a decrease in pH, possibly caused by nitrification. However, this decrease in pH was inhibited by higher SOM content, i.e. SOM mitigated the heavy metal risk from organic fertilizer. In the field experiment, potato (Solanum tuberosum L.) was cultivated using CSS and pig manure (PM). As observed in the pot cultivation, the applied chemical and organic fertilizers increased the soil-soluble and 0.1 N HCl-extractable Zn with increased nitrate. Considering the habitat and the LC50 values of C. japonica that were lower than the concentration of Cu and Zn in the soil solution phase, there is no significant risk from heavy metals in the organic fertilizers. However, the Kd values for Zn were significantly lower for CSS or the PM-applied plot in the field experiment soil, indicating a higher Zn desorption rate from organically fertilized soil particles. The potential risk of heavy metals from agricultural lands under changing climate conditions must therefore be monitored carefully.

Revealing Fungal Diversity in Mesophilic and Thermophilic Habitats of Sewage Sludge Composting by Next-Generation Sequencing

The accumulation of sewage sludge is a severe problem in many countries. Its utilization through composting has the potential to become a widely applied technology. From this perspective, our study investigated the diversity of fungi in mesophilic and thermophilic habitats when composting biosolids, cow manure and wheat straw. It was conducted using a metagenomic approach and next-generation Illumina HiSeq2000 sequencing to reveal the fungal diversity. We found significantly enhanced microbial activity in the thermophilic phase. In contrast, the activity of enzyme β-glucosidase was 29% higher in the mesophilic zone. The range of α-diversity values was more pronounced in the mesophilic habitats than in the thermophilic habitats based on diversity indices. At the class level, the mesophilic fungi were represented by Sordariomycetes—58.7%, Pezizomycetes—15.1% and Agaricomycetes—12.3%, while the most abundant thermophilic fungi found were Sordariomycetes—39.5% and Pezizomycetes—9.8%. In the further clarification of genera diversity, it is striking that at 37.2 °C, Psathyrella was the most abundant with 35.91%, followed by Chaetomidium with 20.11%. Among the thermophiles, Thielavia and Mortierella were the most common. Further research on microbial diversity changes over time is needed to manage the metabolic processes in obtaining quality soil amendment.

Combined addition of bagasse and zeolite stabilizes potentially toxic elements in sewage sludge compost and improves Eucalyptus urophylla seedling growth

Potentially toxic elements (PTEs) including Cu, Zn, Pb, Cd and Ni in sewage sludge compost (SSC) are important obstacles to SSC forestry utilization. Synergistic fixation of bulking agent and adsorbent may shed new light on solving the problem for stabilization of PTEs in SSC before forestry disposal. The aim of this study was to investigate whether bulking agent (bagasse) + adsorbent (zeolite) can be integrated into forestry utilization processes of SSC. First, stabilization of PTEs in SSC were compared to those of composted bagasse + sewage sludge (BSC), zeolite + sewage sludge (ZSC) and bagasse + zeolite + sewage sludge (BZSC) after 60 days of composting. Subsequently, the long-term stability of PTEs in different composts-amended soil was monitored in a 2-year field trial on Eucalyptus urophylla forestland. Finally, a 12-month pot experiment was carried out to investigate their effects on the growth of Eucalyptus urophylla seedlings and PTEs absorption. Compared with SSC, addition of bagasse and zeolite significantly decreased total and extractable PTEs concentration and increased residual fractions in compost. In the field experiment, the total and extractable fraction concentrations of PTEs in topsoil after BZSC application were significantly lower than those after SSC and BSC application, and the status kept unchanged during the 2-year trial period. In the pot experiment, we further found that, compared with SSC, BSC and ZSC addition in the cultivated soil, the addition of BZSC promoted significantly greater growth and reduction in PTEs concentrations in Eucalyptus urophylla seedlings. Our results indicate that the combined addition of bagasse and zeolite can stabilize PTEs in SSC for an extended duration, improve plant growth, and therefore enhance the potential of sewage sludge compost utilization in forestry.

Behavior of trace metals during composting of mixed sewage sludge and tropical green waste: a combined EDTA kinetic and BCR sequential extraction study in New Caledonia.

The aim of the study was to assess the impact of composting on the release dynamics and partitioning of geogenic nickel (Ni), chromium (Cr)and anthropogenic copper (Cu) and zinc (Zn) in a mixture of sewage sludge and green waste in New Caledonia. In contrast to Cu and Zn, total concentrations of Ni and Cr were very high, tenfold the French regulation, due to their sourcing from Ni and Cr enrichedultramafic soils. The novel method used to assess the behavior of trace metals during composting involved combining EDTA kinetic extraction and BCR sequential extraction. BCR extraction revealed marked mobility of Cu and Zn: more than 30% of the total concentration of these trace metals was found in the mobile fractions (F1 + F2) whereas Ni and Cr were mainly found in the residual fraction (F4). Composting increased the proportion of the stable fractions (F3 + F4) of all four trace metals studied. Interestingly, only EDTA kinetic extraction was able to identify the increase in Cr mobility during composting, Cr mobility being driven by the more labile pool (Q1). However, the total mobilizable pool (Q1 + Q2) of Cr remained very low, < 1% of total Cr content. Among the four trace metals studied, only Ni showed significant mobility, the (Q1 + Q2) pool represented almost half the value given in the regulatory guidelines. This suggests possible environmental and ecological risks associated with spreading our type of compost that require further investigation. Beyond New Caledonia, our results also raise the question of the risks in other Ni-rich soils worldwide.

The influence of diverse fertilizer regimes on the phytoremediation potential of Pteris vittata in an abandoned nonferrous metallic mining site

Organic waste comprises a large amount of hydrocarbon containing organic substances, which is regarded as a potential resource rather than simply a waste. A field experiment was conducted in a poly-metallic mining area to investigate the potential of organic waste to facilitate the soil remediation process. Different organic wastes and a commonly used commercial fertilizer were added to heavy metal contaminated soil, which was under phytoremediation using the As hyperaccumulator Pteris vittata. The influence of diverse fertilizer regimes on the biomass of P. vittata and heavy metal removal by P. vittata, was investigated. The soil properties were analyzed after the application of phytoremediation with or without the addition of organic wastes. Results indicated that sewage sludge compost is an appropriate amendment to improve the phytoremediation efficiency. Compared to the control, the application of sewage sludge compost significantly reduced the extractability of As in soil by 26.8 %, and increased the removal of As and Pb by 26.9 % and 186.5 %, respectively. The highest removal of As and Pb reached 33 and 34 kg/ha, respectively. The sewage sludge compost-strengthened phytoremediation improved soil quality. And the diversity and richness of the bacterial community were improved, as represented by the increase in Shannon and Chao index. With improved efficiency and acceptable cost, the organic waste-strengthened phytoremediation can be used to control the risks posed by high concentrations of heavy metals in mining areas.

Variation of Organic Matter and Releasing Risk Assessment of Pentachlorophenol (PCP) in Sewage Sludge Composting

Variation of Organic Matter and Releasing Risk Assessment of Pentachlorophenol (PCP) in Sewage Sludge Composting

Co-composting of sewage sludge with plant biomass, and analysis of microbiome relevant to plant growth promotion

In this study, a pilot-scale co-compositing process using sewage sludge and plant biomass in Japan was used as a model for a local circular bioeconomy. Heavy metal concentrations in the developed sewage sludge compost (NSSC) were lower than the threshold values of composts reported worldwide, and the fiber content was higher (33.6 %) than that of commercial sewage sludge compost (CSSC) (9.7 %), indicating that co-composting with plant biomass resolves the issues associated with sewage sludge. Komatsuna (Brassica rapa var. peruviridis) showed plant growth-promoting effects after fertilizing with NSSC compared to CSSC. The alpha diversities of NSSC were 4- to 6-fold higher than those of CSSC, and several effective biosynthetic gene clusters, such as non-ribosomal peptide synthases, siderophores, and acetoin metabolism, were detected in the predominant microorganisms, suggesting that NSSC may promote plant growth owing to an increase in the presence of antagonistic microorganisms and promotion of microbial interactions in the soil.

The Influence of Sewage Sludge Composts on the Enzymatic Activity of Reclaimed Post-Mining Soil

Mining leads to serious degradation of the ecological values of the landscape. After mining is completed, degraded areas should be reclamated in order to mitigate the destructive effects of mining activities. Effective reclamation aims to initiate soil-forming processes. The paper evaluates the effects of land reclamation in post-mining areas 12 to 14 years after the reclamation process. The assessment was based on a determination of the activity of selected enzymes. Municipal sewage sludge compost (SSC) and compost with a composition of 70% municipal sewage sludge + 30% fly ash (SSFAC) were used as an external source of organic matter in the reclamation. The activity of dehydrogenases, phosphatases, and urease was determined. The fertilization of reclaimed soil with compost caused a significant increase in the activity of the assessed enzymes. Significantly higher dehydrogenase activity was found in the soil treated with SSC. The soil treated with SSFAC was characterized by higher activity of phosphatase and urease. The one-time application of composts from sewage sludge and sludge with fly ash, and the introduction of a mixture of grasses, allow for a permanent reclamation effect. An additional ecological advantage of this reclamation model is waste management, which is part of the circular economy strategy.

Neural Image Analysis for the Determination of Total and Volatile Solids in a Composted Sewage Sludge and Maize Straw Mixture

Waste management is one of most important challenges in environmental protection. Much effort is put into the development of waste treatment methods for further use. A serious problem is the treatment of municipal sewage sludge. One method that is useful for this substrate is composting. However, it is reasonable to compost a sewage sludge mixed with other substrates, such as maize straw. To carry out the composting process properly, it is necessary to control some parameters, including the total solids and volatile solids content in the composted mixture. In this paper, a method for the determination of the total solids and volatile solids content based on image analysis and neural networks was proposed. Image analysis was used for the determination of the colour and texture parameters. The three additional features describing the composted material were percentage of sewage sludge, type of maize straw, and stage of compost maturity. The neural models were developed based on various combinations of the input parameters. For both the total solids and volatile solids content, the most accurate models were obtained using all input parameters, including 30 parameters for image colour and texture and three features describing the composted material. The uncertainties of the developed models, expressed by the MAPE error, were 2.88% and 0.59%, respectively, for the prediction of the total solids and volatile solids content.

Composite Biochar with Municipal Sewage Sludge Compost—A New Approach to Phytostabilization of PTE Industrially Contaminated Soils

The presence of potentially toxic elements (PTEs) in soils can upset the natural balance and increase the risk of PTE incorporation into the food chain. The use of composite biochar with municipal sewage sludge compost (MSSC/C) can be an effective way of both managing waste, such as sewage sludge, and providing an effective additive-supporting phytostabilization processes. The effectiveness of D. glomerata and MSSC/C in the technique of assisted phytostabilization of industrially contaminated soils was determined under the pot experiment conditions. The PTE contents in D. glomerata and the soil were determined using the spectrophotometric method. The addition of MSSC/C to PTE-contaminated soil contributed to an 18% increase in plant biomass and increased the soil pH by 1.67 units, with the PTE concentration being higher in the roots than in the above-ground parts of D. glomerata. The MSSC/C addition had the strongest effect on the reduction in Cd, Cr, and Ni contents in the soil following the completion of the experiment. The current study confirmed the effectiveness of MSSC/C in aiding the phytostabilization processes in PTE-contaminated soils.

Developing a Compost Quality Index (CQI) Based on the Electrochemical Quantification of Cd (HA) Reactivity.

The present work demonstrates the use of Cd2+ as a reactivity probe of the fulvic acids (FAs), humic acids (HAs) and dissolved organic matter (DOM) compost extracts. Significant differences were observed between the extracts, with the HA extract showing the highest reactivity. Comparing the different composts, the largest reactivity variation was again observed for HA then FA and finally DOM extracts. The Cd2+ binding extent was used to calculate the quality of composts and compared with a reference of uncomposted organic fertiliser (FLW), leading to the definition of an operational scale of compost quality. The parameter equivalent mass of fertiliser (mEF) was used for this scale sorted the seven composts from 0.353 to 1.09 kg FLW, for compost of sewage sludge (CSS) and vermicompost of domestic waste (CVDW), respectively. The significance of this parameter was verified through a correlation analysis between binding extent and the effect of compost application on lettuce crop growth in a field trial. The results demonstrate the potentiality of FA and HA extracts as markers of compost bioactivity and the use of Cd2+ as a reactivity probe.

Composted sewage sludge utilization in phytostabilization of heavy metals contaminated soils

In phytostabilization, heavy metal-tolerant plants (e.g.,grasses) can be used to reduce the mobility of heavy metals in soils. The most important step in phytostabilization is the selection of the suitable plant species, in which growth and development can be supported by soil amendments. Sewage sludge compost could be a suitable additive, which provides nutrients for the plant species used for phytostabilization and contributes to an alternative solution for sewage sludge utilization. The aim of the study was to examine the potential of sewage sludge compost in phytostabilization for heavy metal contaminated matrices: identify the optimal ratio of sewage sludge compost to decrease phytotoxicity of the matrices, and assessment of feasible plant species for phytostabilization based on its bioaccumulation properties. In this research, perennial ryegrass (Lolium perenne), broad-leaved sorrel sorrel (Rumex acetosa), lettuce (Lactuca sativa) and cabbage (Brassica oleracea var. capitata) were used for phytotoxicity experiments as well as for testing sewage sludge compost amended phytostabilization of polluted flotation sludge and mine tailings. Sewage sludge compost increased the pH and electric conductivity of the matrices. High salt content and low acidity, altogether with heavy metals caused harmful physiological effects on plant species grown without any compost addition. In the root development test, as in the germination test, the application of 5% sewage sludge compost proved to be optimal. The lower translocation factors of broad-leaved sorrel and perennial ryegrass showed a higher rate of heavy metal accumulation in the roots. Perennial ryegrass, cabbage, and lettuce plant species reached their maximum biomass by adding 5% of sewage sludge compost. Based on the bioaccumulation, translocation and biomass properties, application of perennial ryegrass is recommended for phytostabilization of heavy metal contaminated sites. Furthermore, composted sewage sludge also had a significant effect on the reduction of heavy metal uptake by cabbage and lettuce, which highlights their role as indicator plants in ecotoxicological measurements.

Soluble Elements Released from Organic Wastes to Increase Available Nutrients for Soil and Crops

Member States of the European Union must ban burning arable stubble by 2023 and improve the recycling of organic waste into fertilizers and organic farming practices by 2030. The current lack of nutrients from soils and crops leads to food insecurity, human malnutrition and diseases. Consequently, innovative solutions are required, as technosols are constructed by waste. The objective of this paper is to educate on the nutrients that some pruning residues can provide. This work characterizes elemental composition, nutrients soluble fraction and physical and chemical properties of the following organic wastes: almond tree pruning, commercial peat substrate, olive tree pruning, pine needle, date palm leaf pruning, sewage sludge compost and vine pruning. The results show significant differences between macro (Na, K, Ca, Mg) and micronutrient (Fe, Mn, Cu, Zn) content and their solubility. Sewage sludge compost, olive pruning and pine needle are the three residues with the highest presence of nutrients in their elemental composition. Nevertheless, if a farmer applies pruning residues as a nutritional supplement for crops, it will be key to finding the short-term soluble nutrient rate and synchronizing the nutritional requirement curve of a plant’s life cycle with its nutrient release. Consequently, organic waste (without composting treatment) obtains higher solubility rates, being date palm leaf residue the one with the greatest value. The solubility index of organic wastes can be significant in providing short-term nutrients to crops. Hence, our results can help in choosing the proper waste to enhance plant nutrient supply, mainly K, Ca, Mg and Na for crop nutrition, to ensure efficient biofertilization.

Municipal sewage sludge, aquatic weed compost on soil enzymatic activity and heavy metal accumulation in Kale (Brassica oleracea L.)

Enormous quantities of organic wastes such as sewage sludge (SS) and aquatic weed compost (AWC) are produced in large quantities on the banks of Dal Lake Kashmir. It is a challenging task for authorities to manage them properly. Therefore, the study’s purpose was to evaluate these organic wastes agricultural use potential. The experiment was laid out in a randomized complete block design with three replications comprised of nine treatment combinations of SS, AWC and inorganic fertilizers. In the present study, the conjoint use of SS with chemical fertilizer recorded maximum build-up of soil microbial biomass carbon (MCB), urease and dehydrogenase activity with treatment T1. There were significant correlations between soil MCB and from urease and dehydrogenase activity (r2 = 0.95 and 0.97; P < 0.05), respectively. The micronutrient and heavy metal concentrations in kale exposed to SS and AWC were significantly higher than those in the untreated plants, with the highest concentration found in sole application of SS (T7). However, heavy metal concentrations were within the acceptable limits and did not overcome the maximum phytotoxic levels. The study’s finding leads to conclusion that SS along with chemical fertilizers (T1) can improve the enzymatic activity in soil, quality parameters and nutrient content in plants thereby enhancing the yield.

Antibiotic and heavy metal resistance genes in sewage sludge survive during aerobic composting

Municipal sewage sludge has been generated in increasing amounts with the acceleration of urbanization and economic development. The nutrient rich sewage sludge can be recycled by composting that has a great potential to produce stabilized organic fertilizer and substrate for plant cultivation. However, little is known about the metals, pathogens and antibiotic resistance transfer risks involved in applying the composted sludge in agriculture. We studied changes in and relationships between heavy metal contents, microbial communities, and antibiotic resistance genes (ARGs), heavy metal resistance genes (HMRGs) and mobile genetic elements (MGEs) in aerobic composting of sewage sludge. The contents of most of the analyzed heavy metals were not lower after composting. The bacterial α-diversity was lower, and the community composition was different after composting. Firmicutes were enriched, and Proteobacteria and potential pathogens in the genera Arcobacter and Acinetobacter were depleted in the composted sludge. The differences in bacteria were possibly due to the high temperature phase during the composting which was likely to affect temperature-sensitive bacteria. The number of detected ARGs, HMRGs and MGEs was lower, and the relative abundances of several resistance genes were lower after composting. However, the abundance of seven ARGs and six HMRGs remained on the same level after composting. Co-occurrence analysis of bacterial taxa and the genes suggested that the ARGs may spread via horizontal gene transfer during composting. In summary, even though aerobic composting is effective for managing sewage sludge and to decrease the relative abundance of potential pathogens, ARGs and HMRGs, it might include a potential risk for the dissemination of ARGs in the environment.

Metais pesados no solo e em mamoneira adubada com lodo de esgoto submetido a diferentes processos de estabilização

ABSTRACT: This study evaluated the levels of heavy metals in the soil and castor bean plant after fertilization with sewage sludge (SS) subjected to different stabilization processes. The study was conducted in a Haplic Cambisol with the following treatments: control (CO), fertilization with solarized sewage sludge (SSS), composted sewage sludge (CSS), vermi composted sewage sludge (VSS), limed sewage sludge (LSS), and mineral fertilizer (MF). The experimental design included a subdivided plot scheme with fertilization being the primary factor and soil layers or leaf parts being the secondary factor. The data obtained were analyzed using analysis of variance and the Scott-Knott test with 5% significance. Fertilization with SSS, CSS, and LSS led to the highest increase in Zn in the soil, mainly in the surface layer. In the leaf tissues, Zn and Cu levels were higher with the CO and SSS treatments, whereas the Ni level was higher with SSS, CSS, VSS, and MF treatments. In general, Zn and Cu levels were higher in the leaf limb than in the petiole, whereas Ni, Pb, and Cr levels were higher in the petiole than in the leaf limb. In any case, no symptoms of toxicity in the plants and no risk of soil contamination were observed with any of the fertilization treatments.

Effects of biochar on the degradation of organophosphate esters in sewage sludge aerobic composting.

In this study, the impact of biochar on the degradation of organophosphate esters (OPEs) during the aerobic composting of sewage sludge was investigated. Three treatments were conducted with different percentages of biochar in the compost, including 5 %, 10 %, and 20 %. The treatment with 10 % of biochar showed the longest thermophilic phase compared to that of 5 % and 20 % of biochar, which greatly promoted the decomposition of organic matter. In addition, the degradation rate of the hard-to-degrade chlorinated-OPEs was significantly increased by 10 % biochar, reaching to 57.2 %. Correspondingly, approximately 43.6 % of the total concentration of OPEs (Σ6OPEs) was eliminated in the presence of 10 % of biochar, which was higher than the treatments with 5 % and 20 % of biochar. Biochar significantly influenced the microbial community structure of compost, but the previously reported organophosphorus-degrading bacteria did not play a major role in the degradation of OPEs. The redox ability of the increased oxygen-containing functional groups such as quinone on the surface of biochar and the biochar-mediated electron transfer ability may play an essential role in the degradation of OPEs during the composting process.